A datacenter/cloud facility typically contains thousands of servers that demand large amounts of power for both server operation and cooling, leading to high operating cost and hidden cost associated with the facility's carbon footprint. Cloud providers are faced with a challenging problem of running energy-efficient data centers. Meanwhile, the workload experienced by the servers varies through the day. If the servers are on all of the time, the utilization would be dramatically low during period of less active workload because datacenter capacity is usually provisioned for peak rather than average load.